1. Field of the Invention
The invention pertains to the field of tensioners. More particularly, the invention pertains to a tensioner that has damping.
2. Description of Related Art
FIG. 1 shows a prior art chain driving system having a blade tensioner and a guide. A closed loop chain encircles driving sprocket 12 and driven sprocket 10. Each sprocket 10, 12 accelerates and decelerates independently while maintaining forward motion. A fixed guide 14 is attached to a bracket 7 on the tight strand of the chain. Opposite the guide 14 on the slack strand of the chain is a tensioner 16, which is at least semi-rigidly fixed to the bracket 7 and biased towards the tight strand of the chain. Bolts 18 fasten the bracket containing the tensioner 16 and the guide 14 to the engine block (not shown).
When the driving sprocket 12 accelerated or the driven sprocket 10 decelerates, an energy wave or high local load is created in the tight strand of the chain, which travels from the sprocket that changed in velocity toward the other sprocket. The chain 8 attempts to span the distance between the link of the chain in contact with the initiating sprocket to the other sprocket in the shortest possible distance, a straight line. The energy moves through the links on the free strand of the chain until it comes to the end of the guide 14, which absorbs the energy. As a result from the constant absorption of the high local load the ends of the guide 14 sustains significant wear. The energy wave would be present and show the same characteristics if it was to originate on the slack strand of the chain, although the wave energy may not occur at all depending on how well the tensioner keeps the slack out of the chain and how much damping the tensioner has.
One solution to reduce the load that results in the prior art chain driving system is to add damping to the tensioner. One problem associated with adding the required damping to a tensioner is that if the tensioner is softened significantly, it may result in a loss of chain control, since tensioners are specifically designed to apply just enough force to provide adequate chain control. Other solutions are shown in U.S. Pat. Nos. 5,180,340, 5,797,818, and 5,976,922, 6,322,470, as well as U.S. application Ser. No. 2002-0045503 and Japanese Application No. 2003-047652.
U.S. Pat. No. 5,180,340 discloses a coil spring attached to a block on the slack side and tight side of the chain that biases an ejector/apex which is located on the inside side of the chain. As force is applied to the ejector/apex, the ejector pivots against the biasing action of the coil spring to swing toward the adjacent sprocket.
U.S. Pat. No. 5,797,818 discloses a chain assembly with reduced noise and vibration on the slack side of the chain comprising a blade shoe, a spring, and a resilient damping device. The shoe is pivotally mounted to the tensioner bracket. The spring is mounted to the shoe and biases the shoe towards the chain. The resilient damping device is mounted between the tensioner bracket and the spring to aid in controlling the vibration that occurs during valve events.
U.S. Pat. No. 5,976,922 discloses a tensioning device comprising a tension lever that has first and second slide blocks affixed, such that the slide blocks are on either side of the slack side of chain. The first slide block is pivotably attached to a guide rail on the tight side of the chain. The second slide block is biased against one of the sides of the slack side of the chain by a tension element comprising a compression spring and a piston.
U.S. Pat. No. 6,322,470 discloses a tensioner that includes a pair of pivoting arms used to simultaneously tension two separate strands of the same chain. A lever with fixed pins is located between the two strands. The arms extend outside the strands of the chain and carry shoes positioned to contact the outside portion of the chain are pivotally mounted to the fixed pins. Rotation of the lever causes the fixed pins to move laterally and the arms draw inward and tension is imparted to the separate chain strands at the same time. In other words, a high load on one side of the chain tries to transfer to the other side of the chain but the load eventually evens out.
US 2002-0045503 discloses a chain tensioner that has a blade and spring assembly. The blade has a first end and a second end. The first end defines a hub. The hub is connected to the central portion of the blade shoe and a first end wall and defines a bore that receives a pin that pivotably connects the blade to a mounting bracket.
Japanese Application No. 2003-074652 discloses a tensioner in which a support member is turnably pivoted on a center line connected the two sprockets. Attached to the support member are pressing members on either side of the chain at the same time. The damping that occurs of the slack and tight side of the chain is individual to each side of the chain, since each of the pressing members floats relative to the chain. While there is only one pivot present between the two pressing members, the load on one tries to affect the other and the pressing members undulate back and forth on the chain.